77mm Filter Size f/4 Aperture N/A Stabilized EF Mount The Canon EF 17-40mm f4L USM Lens is an affordable L-series ultra-wide-angle zoom lens that's ideal for both film and digital SLRs. Superior optics are assured by the use of three aspherical lens elements, in addition to a Super UD (Ultra-low Dispersion) glass element. Optical coatings are optimized for use with digital cameras. This lens focuses as close as 11 inches (0.28m), and offers both Canon's full-time manual focus and a powerful ring-type USM for fast and silent AF. It has a constant f/4 maximum aperture, and offers the choice of screw-in 77mm filters or a holder in the rear of the lens for up to three gel filters. Finally, it offers weather-resistant construction similar to other high-end L-series lenses Optical coatings optimized for digital cameras Close focus to 11 inches Super UD and three Aspherical lens elements ensure superior image quality Dust- and moisture-resistant, constructed for professional use

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